Some 380 million years ago, a few pioneering vertebrates
first made the leap from water to land. And today, tens of millions
of their human descendants seek summer amusement by leaping the other
way. According to the travel industry,
>close to 90 percent of vacationers choose as their holiday destination
an ocean, lake or other scenic body of water.
We may have lungs rather than gills, and the weaker swimmers among us
may be perfectly >capable of drowning in anything deeper than a bathtub,
yet still we feel the primal tug of the tide. Consciously or otherwise,
we know were really all wet.
As fetuses, we gestate in bags of water. As adults, we are bags of water:
roughly 60 percent of our body weight comes from water, the fluidic
>equivalent of 45 quarts. Our cells need water to operate, and because
we lose traces of our
internal stores with every sweat we break, every breath and excretion
we out-take, we must constantly consume more water, or we will die in
Thirstiness is a universal hallmark of life. Sure, camels can forgo
drinking water for five or six months and desert tortoises for that
many years, and some bacterial and plant spores seem able to survive
for centuries in a state of
dehydrated, suspended animation. Yet sooner or later, if an organism
plans to move, eat or multiply, it must find a solution of the aqueous
Life on Earth arose in water, and scientists cannot imagine life arising
elsewhere except by waters limpid grace. In the view of Geraldine
Richmond, a chemistry professor at the University of Oregon who often
talks to the public on the wonders of water, Mark Twain put it neatest:
Whiskey is for drinking; water is for fighting over.
Behind waters peerless punch, and the reason it rather than alcohol
or any other lubricant serves as the elixir of life, is the three-headed
character whose chemical name we all know: H2O. Scientists observe that
when two atoms of hydrogen conjoin with one of oxygen, the resulting
molecule displays a spectacular range of powers, gaining the mightiness
of a molecular giant while retaining the speed and convenience of a
Water behaves very differently from other small molecules,
said Jill Granger, a professor of chemistry at Sweet Briar College in
Virginia. If you want something else with similar properties,
youd end up with something much bigger and more complex, and then
youd lose the advantages that water has in being small.
Because of waters atomic architecture, the tendency of its comparatively
forceful oxygen centerpiece to cling greedily to electrons as it consorts
with its two meeker hydrogen mates, the entire molecule ends up polarized,
electromagnetic charges on its foreside and aft. Those mild charges
in turn allow water molecules to engage in mild mass communion, linking
up with one another and with other molecules, too, through an essential
connection called a hydrogen bond. The hydrogen bond that attracts water
to water and to other like-minded players is subtler than the bond that
ties each water molecules atoms together. But subtlety breeds
opportunity, and from hydrogen bonds many of waters major and
minor properties flow.
With their hydrogen bonds, water molecules become sticky, cohering as
a liquid into droplets and rivulets and following each other around
like a jiggling conga line. Such stickiness means that water is drawn
to the inner plumbing of plants and will crawl up the fibrous conduits
to hydrate even the crowns of redwood trees towering hundreds of feet
Pulled together by hydrogen bonds, water molecules become mature and
stable, able to absorb huge amounts of energy before pulling a radical
phase shift and changing from ice to liquid or liquid to gas. As a result,
water has surprisingly high boiling and freezing points, and a strikingly
generous gap between the two. For a substance with only three atoms,
and two of them tiny little hydrogens, Dr. Richmond said, youd
expect water to vaporize into a gas at something like minus 90 degrees
Fahrenheit, to freeze a mere 40 degrees below its boiling point, and
to show scant inclination to linger in a liquid phase.
Thats what happens to hydrogen sulfide, a similarly sized molecule
but with its two hydrogen atoms fastened to sulfur rather than to oxygen;
on our temperate world, hydrogen sulfide has long since reached its
boiling point and exists as a foul-smelling gas. Same for the tidy troika
of carbon dioxide: low freezing point, low boiling point, and, poof,
its up in the air. But given its vivid power of hydrogen bonding,
water proves less flighty and fickle, with a boiling point at sea level
of 212 degrees Fahrenheit, and a full 180 degrees lying between the
tempest of a teapot and the tinkling of an
ice cube at 32 degrees. A vast temperature span over which water molecules
can pool and cling as the liquid assets we love best.
We rely in myriad ways on waters fluid forbearance, its willingness
to take the heat without blinking. Earths oceans and lakes soak
up huge quantities of solar radiation and help moderate the climate.
As sweat evaporates from
our skin, it wicks away large amounts of excess heat.
Water also serves as a nearly universal solvent, able to dissolve more
substances than any other liquid. It can act as an acid, it can act
as a base, with a pinch of salt it is the solution in which the cells
thousands of chemical reactions take place.
At the same time, waters gregariousness, its hydrogen-bonded viscosity,
helps lend the cell a sense of community.
Water acts as the contact between biological molecules, not just
separating them, but imparting information among them, said Martin
Chaplin, a professor of applied science who studies the structure of
water at London South Bank University. In an aqueous environment,
all the molecules are able to feel the structure of all the other molecules
that are present, so they can work as whole rather than as individuals.
Theres no end to waters chemical kinkiness, including the
way it freezes from the top down and becomes buoyant as it chills. Most
substances shrink and get denser and heavier as they cool, and expand
and lighten as they melt. Water bucks the norm, and is lighter and airier
as ice than when liquid, and so in winter marine life can find liquid
haven beneath the floating blanket of ice, and so in summer ice cubes
bob and clink in your glass of lemonade. Bottoms up.